Brachytherapy procedures for treatment of prostate cancer are well known. Brachytherapy involves treating cancer by precisely locating a plurality of radiation sources (e.g., pellets of a radioactive isotope or "seeds") inside a human body in a three-dimensional array. Small amounts of a radioactive isotope, such as iodine-125 or palladium-103, are encapsulated in a suitable casing to form the seeds which are implanted. The seeds are placed in the treatment area according to a seed placement plan.
At least four major steps are performed in a brachytherapy procedure for the treatment of prostate cancer using a perineal approach to the prostate guided by, for example, transrectal ultrasonography. First, a transrectal ultrasound study or other suitable imaging technique is used to gain information concerning the location, size and positioning of a patient's prostate, surrounding tissues and surrounding organs. The imaging of the structures may be in the form of a visual image on a suitable medium or in the form of electronic data. In the former case the image may be captured as, for example, an ultrasound film or ultrasound Poloroid.RTM. scan which is then digitized by manually outlining the desired features. In the latter case, for example, raw ultrasound data may be captured and stored in electronic format. Ultrasound data may also be in the form of a VCR tape of an ultrasound study.
Second, a pre-implantation seed placement plan is developed to determine the desired location of the seeds in a three-dimensional space. A goal of the seed placement plan is to enable sufficient doses of radiation to impinge on the target structures or portions of structures needing treatment, while minimizing radiation to other structures or portions of structures in and near the treatment area, such as healthy tissue of the adjacent rectum and bladder. General criteria for establishing seed placement plans is known. In general, the process of generating a seed placement plan involves proposing the location of a plurality of seeds in a three-dimensional space, and, based on the known radiation characteristics of the seeds, calculating the radiation dose levels within the treatment area resulting from the proposed seed placement. The effectiveness of the proposed plan may conveniently be determined through the use of isodose lines which may be displayed for the user. Various revisions to the plan and reevaluation may be made in an attempt to optimize the plan. Each iteration of revisions to the plan and reevaluation is time consuming since it requires recalculation of the dosimetry and the expected results for each proposed placement plan.
Once an acceptable plan is developed, the third step is to physically implant the seeds according to the optimized seed placement plan and using known brachytherapy protocols. The seeds are typically delivered and positioned using needles which are inserted through a catheter or microcatheter. One method of increasing the accuracy of placement involves placing a needle guide template over the perineum to assist the physician in placing the seeds in the patient's prostate. The needle guide template is a physical device of known geometry containing holes with predetermined (e.g., half-centimeter) spacing. The needle guide template may be registered by identifying two known landmarks in a captured image and accounting for any relative translation, rotation, or scaling of the image.
The last major step in the procedure may include a post-implant evaluation procedure. In this step, the actual location of the seeds is determined and compared with the intended seed location as specified in the seed placement plan. To do this, post-implementation images of the treatment area are taken, so that the actual location of each seed can be identified. Imaging techniques which are distinct from those used for pre-implantation are typically used during the post-implantation phase. After obtaining the post-implantation imaging, a comparison of each seed's planned location with its actual location may be made. If necessary, further implantation may be performed or the previous implantation locations may be adjusted according to medically known procedures.
Computer implemented systems for assisting with some or all of the above steps are known. Software for one such system is available from Multimedia Medical Systems, the assignee of the present invention, and others. One such system is marketed by the assignee as MMS TherpacPLUS.upsilon. Version 6.5. These known systems are useful in assisting with certain aspects of the pre-implantation plan and the post-implantation evaluation, but have various limitations and drawbacks.
While known systems are generally effective in developing and implementing a seed placement plan according to the specific aspects of each patient's physiological makeup, they are often deficient when it is necessary or desirable to develop multiple, alternative seed placement plans and work with them over time until the most beneficial plan is selected for implementation. This is especially true in connection with complex placement plans that require multiple iterations to optimize. In particular, known systems do not typically permit user-friendly and efficient evaluation, storage and selection between and among multiple seed placement plans.